Field of the Invention
The present invention relates to a method of monitoring a dressing process of a polishing pad for polishing a substrate, such as a wafer. The present invention further relates to a polishing apparatus.
Description of the Related Art
A polishing apparatus, which is typified by a CMP apparatus, is configured to polish a substrate by moving a polishing pad and a surface of the substrate relative to each other while supplying a polishing liquid onto the polishing pad attached to a polishing table. In order to maintain a polishing performance of the polishing pad, it is necessary to regularly perform dressing (or conditioning) of a polishing surface of the polishing pad by a dresser.
The dresser has a dressing surface with diamond particles secured to the dressing surface in its entirety. The dresser includes a removable dress disk whose lower surface serves as the dressing surface. The dresser is configured to press the polishing surface of the polishing pad while rotating about its own axis and moving on the polishing surface. The rotating dresser scrapes away the polishing surface of the polishing pad slightly, thereby regenerating the polishing surface of the polishing pad.
An amount of the polishing pad (i.e., a thickness of the polishing pad) scraped away by the dresser per unit time is called a cutting rate. It is desirable that the cutting rate be uniform over the polishing surface of the polishing pad in its entirety. In order to obtain an ideal polishing surface, it is necessary to perform a recipe tuning of the pad dressing. In this recipe tuning, a rotational speed and a moving speed of the dresser, a load of the dresser on the polishing pad (which will be hereinafter referred to as a dressing load), and the like are adjusted.
In order to evaluate a surface condition of the polishing pad that has been dressed by the dresser, it is necessary to measure the thickness of the polishing pad after removing it from the polishing table. Moreover, the surface condition of the polishing pad cannot be evaluated until a substrate is actually polished. Accordingly, the recipe tuning of the pad dressing entails consumption of a lot of polishing pads and times.
There have been proposed several methods of evaluating the dressing process by measuring the cutting rate and the dressing load. However, these methods achieve the evaluation of the dressing process by estimating an actual dressing process from the dressing results and the dressing load, and cannot monitor the dressing process itself.